With the rapid development of the Internet and the popularity of large-screen multi-function mobile phones, there have been a large number of mobile data multimedia services and a variety of broad bandwidth multimedia services such as: video conferencing, TV broadcasting, video on demand, advertising, online education, interactive games, and so on, which meets the increasing service needs of the mobile users on the one hand, and meanwhile brings new service growth point for mobile operators. These mobile data multimedia services require multiple users to simultaneously receive the same data, compared with typical data services, it has features such as large data amount, long duration and delay sensitivity.
In order to effectively use the mobile network resources, the third Generation Partnership Project (3GPP) proposes the MBMS service, this service is a technology of transmitting data from one data source to multiple targets to achieve the sharing of the network (including the core network and access network) resources and to improve the utilization of the network resources (especially the air interface resource). The MBMS service defined in the 3GPP can achieve the broadcast and multicast of not only the low-speed text messages but also the high-speed multimedia services, so as to provide a variety of enriched videos, audios and multimedia services, which undoubtedly conforms to the future mobile data development trends and provides better service prospects for the 3G development.
The Long Term Evolution (LTE) Release 8/9 specifies using the MBSFN sub-frame to transmit the MBMS service, but not all MBSFN sub-frames are used to transmit the MBMS service, for example, some MBSFN sub-frames are also used for positioning service, relay service, and so on. It should be noted that, so far only the multi-cell transmission MBMS service is considered in the LTE Release 8/9, while the single-cell transmission MBMS service is not considered, and to date, the multi-cell transmission MBMS service must use the MBSFN sub-frame to bear and send, while the single-cell transmission MBMS service might use the MBSFN sub-frame to bear and send. Wherein, the specific definition of the multi-cell transmission MBMS service can refer to the 36.331 protocol, and the basic feature thereof is sending the MBMS service via the Physical Multicast Channel (PMCH) or bearing the MBMS service via the Multicast Channel (MCH).
Currently, the LTE specifies using the two-level method to configure the radio frames and sub-frames bearing the MBMS, and the method is described as follows:
The first level implements the configuration of the radio frames bearing the MBMS, and it meets the following equation:SFN mod radioFrameAllocationPeriod=radioFrameAllocationOffset
Where, SFN is the abbreviation of System Frame Number, that is, the system radio frame number, from 0 to 1023; radioFrameAllocationPeriod denotes the MBSFN radio frame period which can be any value from {1, 2, 4, 8, 16, 32}; radioFrameAllocationOffset is the MBSFN radio frame offset and its value is smaller than the selected MBSFN radio frame period and is an integer no less than 0; “mod” denotes acquiring the modulus or remainder of the SFN to the radioFrameAllocationPeriod. The radio frames configured for bearing the MBMS service are called the MBSFN radio frames.
The second level achieves the configuration of the sub-frames bearing the MBMS service in the MBSFN radio frames, generally using the bitmap method. As specified in the LTE, the sub-frames #0, #4, #5 and #9 in the frequency division duplex (FDD) mode cannot bear the MBMS service, nor do the sub-frames #0, #1, #5 and #6 in the time division duplex (TDD) mode, thus, the 6-bit bitmap is used to describe which ones in the remaining six sub-frames are used to bear the MBMS service, and the configurations of the sub-frames bearing the MBMS service in each MBSFN radio frame are the same. As the two-level configuration signaling is sent in the Broadcast Control Channel (BCCH) to the terminal, the configurations of the sub-frames in the MBSFN radio frames in each BCCH modification period cannot be changed. The aforementioned sub-frame bearing the MBMS service in the MBSFN radio frame is called MBSFN sub-frame, also known as multicast sub-frame.
The MBSFN sub-frames used to bear the MBMS service use the extended cyclic prefix, such MBSFN sub-frame has 12 OFDM symbols, where the first one or two OFDM symbols are used for transmitting the control information of the unicast service, also known as Physical Downlink Control Channel (PDCCH), the remaining resources in such sub-frame are used to send the MBMS service, in the current LTE R9, the scheduling of the MBMS service is a semi-static scheduling, and the MBMS service in this period is achieved via the scheduling period. Thus, the MBMS is configured once in one period, that is, at the beginning of each scheduling period, the system needs to allocate resources for sending the MBMS service in this scheduling period and assign what specific MBMS service will be sent in which resources, all these are uniformly configured by each cell in the MBSFN domain.
In general, to send the MBMS service in one MBSFN domain, it needs each cell participating the sending provides the same idle resources, and the MBMS service is sent on the same resources. If any cell A in the MBSFN domain cannot provide the same resources, then the MBMS service cannot be sent in these resources within the entire MBSFN domain, or, if the MBMS service is sent in this case, the performance of other services sent by the cell A in these resources will be affected. In the present invention, the 2nd OFDM symbol in the MBSFN sub-frame happens to have the similar problem, that is, the 2nd OFDM symbol in such a sub-frame potentially has the risk of being unable to send the MBMS service, and the specific analysis is as follows:
First of all, the characteristics and the necessary conditions for the MBMS service transmission of the multi-cell transmission MBMS service are given: multi-cell transmission MBMS service is characterized by using the MBSFN combination method to air interface combine the data of the same MBMS service sent by each cell in the MBSFN domain. In view of this, the transmission of the multi-cell transmission MBMS service must meet the following conditions, in short, the electromagnetic waves of the MBMS data sent by each cell involved in transmitting the MBMS service in the MBSFN domain should be identical, so that the electromagnetic signals from different cells can be naturally superposed in the air to enhance the signal performance. Specifically, the same frequency and time resources are used to send the data in the same format.
Second, analyzing the number of OFDM symbols occupied by the PDCCH of each cell. In short, the number of OFDM symbols occupied by the PDCCH of each cell is decided by the cell itself, for example, the number of OFDM symbols occupied by the PDCCH of each cell is decided according to the number of user terminals in the cell or the characteristics of the user terminals (such as multi-antenna terminals). For example, each cell determines the number of OFDM symbols used by its PDCCH according to the number of users to be scheduled in the cell at this time, that is, when the local cell has a relatively large number of users to be scheduled, the PDCCH uses the first two OFDM symbols, otherwise, the PDCCH uses the first one OFDM symbol while not the second one. Specifically, the 2nd OFDM symbol might be occupied by the PDCCH, and whether it is occupied or not is mainly determined by the cell itself, therefore, in a MBSFN domain, the PDCCH of some cells occupy the first two OFDM symbols in the MBSFN sub-frame, while others only occupy the 1st OFDM symbol in the MBSFN sub-frame. With the increasing number of cells in the MBSFN domain, it is difficult to find at one MBSFN sub-frame in this MBSFN domain that the PDCCH of all cells in the domain occupies the first two OFDM symbols or the 1st OFDM symbol. Only when the PDCCH of all cells occupies the 1st symbol can the 2nd OFDM symbol of this MBSFN sub-frame be used to transmit the MBMS service, however, the probability of this case is very small.
A scenario is given in the following to illustrate that the 2nd OFDM symbol is potentially unable to send the MBMS service. For example, FIG. 1 illustrates an example that there are multiple cells in the MBSFN domain, as shown in FIG. 1, if all the cells in the MBSFN domain in the figure are involved in the transmission of the MBMS service and cell 1 and cell 2 need to schedule a relatively large number of users, the PDCCH of the cell 1 and the cell 2 use the first two OFDM symbols, while the PDCCH of other cells in the domain only use the first one OFDM symbol. In this case, the 2nd OFDM symbol is not the resources shared by multiple cells in the MBSFN domain, and the cells in the MBSFN domain cannot use the 2nd OFDM symbol to send the MBMS service, which will result in system resource waste; If the 2nd OFDM symbol is forced to send the MBMS service, since the multi-cell transmission MBMS service has air interface superimposed gain, the PDCCH information transmitted in the 2nd OFDM symbol by few cells (for example, the cell 1 and the cell 2) will be strongly interfered with each other because most cells send the MBMS data in the 2nd OFDM symbol, so that the PDCCH information of these few cells cannot be received normally.